Composite photoresist structure

ABSTRACT

A composite photoresist structure includes a first organic layer disposed over a substrate to be etched, a sacrificial layer disposed on the first organic layer, and a second organic layer disposed on the sacrificial layer. The thickness of the first organic layer and the thickness of the second organic layer are both larger than the thickness of the sacrificial layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/465,811, filed Aug. 20, 2006, which itself is a continuation of U.S.application Ser. No. 10/708,983, filed Apr. 5, 2004. Additionally,application Ser. No. 10/708,983 is itself a divisional of U.S.application Ser. No. 10/063,307, filed Apr. 10, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoresist structure, and moreparticularly, to a photoresist structure suitable for sub-micron patterntransfers in semiconductor processes.

2. Description of the Prior Art

Generally, integrated circuit production relies on the use ofphotolithographic processes and etching processes to define variouselectrical elements and interconnecting structures on microelectronicdevices. With the coming of a generation of Ultra Large Scale Integrated(ULSI) Circuits, the integration of semiconductor devices has gottenlarger and larger. G-line (436 nm) and I-line (365 nm) wavelengths oflight have been widely used in photolithography processes. However, inorder to achieve smaller dimensions of resolution, wavelengths of lightused for photolithography processes have been reduced into deep UVregions of 248 nm and 193 nm. Nevertheless, the shorter the wavelengthsof light are, the thinner the photoresist layers are. The thinphotoresist layers might not be thick enough for blocking the etchingprocesses in the following fabrication. As a result, for aphotolithography process utilizing short wavelengths of light, it isnecessary to look for a photoresist structure suitable for lithographyprocesses and etching processes.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior artphotoresist structure. As shown in FIG. 1, a semiconductor wafer 10comprises a substrate 12, an anti-reflection layer 14, and a photoresistlayer 16. Because wavelengths of light used for exposure processes arerelated to the depth of focus (DOF), a required thickness of thephotoresist layer 16 depends on the wavelengths of light. Accordingly,the thickness of the photoresist layer 16 has to be thin enough so thatthe molecules in the surface of the photoresist layer have approximatelythe same focus as the molecules in the bottom of the photoresist layer.However, the photoresist layer 16 is used to be a hard mask on thesubstrate 12 in the following etching processes. For this reason, thethin photoresist layers might not be thick enough for blocking thefollowing etching processes.

Please refer to FIG. 2. FIG. 2 is a schematic diagram of another priorart photoresist structure used to overcome the above-mentioned problem.As shown in FIG. 2, a semiconductor wafer 20 comprises a substrate 22, asilicon oxynitride layer 24, an anti-reflection layer 26, and aphotoresist layer 28. Therein the silicon oxynitride layer 24 serves asa hard mask so that the photoresist layer 28 together with the siliconoxynitride layer 24 can block the etching processes in the followingfabrication. After the predetermined pattern of the mask is transferredonto the substrate 22, the silicon oxynitride layer 24, theanti-reflection layer 26, and the photoresist layer 28 are removed.However, the silicon nitride layer 24 is not easy to etch away. Thus,the process of removing the silicon nitride layer 24 usually causesdamage to the surface of the substrate 22.

In addition, methods used to overcome the above-mentioned problemfurther include bi-layer photoresist technology (U.S. Pat. No.6,323,287) and top surface image (TSI) technology (U.S. Pat. No.6,296,989). However, both of the two methods require new photoresistmaterials. For example, the photoresist layer used in the TSI technologycomprises silicon-containing materials. Providing new photoresistmaterials will increase production costs and increase complexity anddifficulty of processes. As a result, it is necessary to look for aphotoresist structure suitable for sub-micron pattern transfers inphotolithography processes and etching processes.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the claimed invention to providea composite photoresist structure so as to solve the above-mentionedproblem.

According to the claimed invention, a composite photoresist structureincludes a first organic layer disposed over a substrate to be etched, asacrificial layer disposed on the first organic layer, and a secondorganic layer disposed on the sacrificial layer. The thickness of thefirst organic layer and the thickness of the second organic layer areboth larger than the thickness of the sacrificial layer.

It is an advantage over the prior art that the claimed inventionprovides a composite photoresist structure including a first organiclayer, an inorganic sacrificial layer, and a second organic layer. Thefirst and second organic layers are both thicker than the sacrificiallayer. Furthermore, a thickness of the second organic layer can beadjusted according to wavelengths of light sources used in exposureprocesses. Simultaneously, by adjusting thicknesses of the sacrificiallayer and the first organic layer, the composite photoresist structureis thick enough to block following etching processes. Thus, the claimedphotoresist structure is suitable for sub-micron pattern transfers insemiconductor processes. In addition, the first organic layer isregarded as a hard mask and it is easily removed by use of plasma. It isa further advantage that removing the first organic layer will notdamage the substrate.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a prior art photoresist structure.

FIG. 2 is a schematic diagram of another prior art photoresiststructure.

FIG. 3 is a schematic diagram of a composite photoresist structureaccording to the present invention.

FIG. 4A to FIG. 4F are schematic diagrams illustrating an etchingprocess utilizing the composite photoresist structure.

FIG. 5 is a schematic diagram of a composite photoresist structureaccording to another embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 3. FIG. 3 is a schematic diagram of a compositephotoresist structure according to the preferred embodiment of thepresent invention. As shown in FIG. 3, a composite photoresist structure30 comprises a first organic layer 30 a, a sacrificial layer 30 blocated on the first organic layer 30 a, and a second organic layer 30 clocated on the sacrificial layer 30 b. The first organic layer 30 a andthe second organic layer 30 c both comprise organic materials. Thesacrificial layer 30 b comprises inorganic materials. In addition, thethickness of the first organic layer 30 a and the thickness of thesecond organic layer 30 c are both larger than the thickness of thesacrificial layer 30 b. Furthermore, the thickness of the first organiclayer 30 a is also larger than the thickness of the second organic layer30 c.

In particular, the first organic layer 30 a is made of low dielectricorganic materials, such as SiLK™. Additionally, the first organic layer30 a is also made of spin-on glass (SOG). Consequently, it is easy toremove the first organic layer 30 a by means of plasma, which includesoxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon (Ar), C_(x)F_(y),C_(x)H_(y)F_(z), or helium (He) plasma. The sacrificial layer 30 b ismade of inorganic anti-reflection materials such as silicon oxynitride(SiON) and silicon nitride (SiN). In addition, the sacrificial layer 30b is also made of materials used for conventional hard masks, such assilicon nitride and silicon oxide. Moreover, the second organic layer 30c is made of organic photoresist materials that include positivephotoresist materials and negative photoresist materials. Furthermore,the second organic layer 30 c is made of organic materials suitable forutilizing in the e-beam lithography process. Noticeably, the compositephotoresist structure 30 is suitable for any photolithography processesin the semiconductor fabrication. It should be known by one skilled inthe art that a thickness of each of the first organic layer 30 a, thesacrificial layer 30 b, and the second organic layer 30 c could beadjusted according to requirements of processes.

Please refer to FIG. 4A to FIG. 4F. FIG. 4A to FIG. 4F are schematicdiagrams illustrating an etching process utilizing the compositephotoresist structure 30. As shown in FIG. 4A, a semiconductor wafer 40comprises a substrate 42 and the composite photoresist structure 30formed on the substrate 42. The substrate 42 is a silicon substrate, ametal substrate or a dielectric layer, which has a planar and smoothsurface. Firstly, as shown in FIG. 4B and FIG. 4C, an exposure processand a development process are performed to transfer a predeterminedpattern onto the second organic layer 30 c. Then, using the secondorganic layer 30 c as an etching mask, a dry etching process isperformed on the sacrificial layer 30 b in order to transfer thepredetermined pattern in the second organic layer 30 c onto thesacrificial layer 30 b. Besides, in another embodiment of the presentinvention, the predetermined pattern can be formed in the second organiclayer by utilizing the e-beam lithography process.

As shown in FIG. 4D to FIG. 4F, utilizing the sacrificial layer 30 b tobe an etching mask, an anisotropic etching process is performed totransfer the predetermined pattern onto the first organic layer 30 a.Then, using the sacrificial layer 30 b and the first organic layer 30 aas an etching mask, an etching process is performed to transfer thepredetermined pattern in the first organic layer 30 a onto the substrate42. While etching the substrate 42, the sacrificial layer 30 b isremoved concurrently. After transferring the predetermined pattern ontothe substrate 42, the first organic layer 30 a is subsequently removed.Up to now, the predetermined pattern on the mask is thoroughlytransferred onto the substrate 42. The first organic layer 30 a isregarded as a hard mask, and its thickness can be adjusted in order toblock subsequent etching processes. Thus, the composite photoresiststructure 30 can be used in a photolithography process utilizing lightsources with wavelengths shorter than 248 nm in deep UV regions.Furthermore, conventional hard masks are generally made out of siliconnitride or silicon oxide, which are not easy to etch away. Hence, anacidic trough is required to remove the conventional hard masks.Conversely, it is easy to remove the first organic layer 30 a throughuse of plasma. Furthermore, removing the first organic layer 30 a willnot damage the substrate 42.

Please refer to FIG. 5. FIG. 5 is a schematic diagram of a compositephotoresist structure according to another embodiment of the presentinvention. As shown in FIG. 5, a composite photoresist structure 50comprises a first organic layer 50 a, a sacrificial layer 50 b locatedon the first organic layer 50 a, an anti-reflection layer 50 c locatedon the sacrificial layer 50 b, and a second organic layer 50 d locatedon the anti-reflection layer 50 c. The first organic layer 50 a is madeof low dielectric organic materials. In addition, the first organiclayer 50 a can be made of spin-on glass (SOG). It is easy to remove thefirst organic layer 50 a by use of plasma. The sacrificial layer 50 b ismade of materials used for hard masks such as silicon nitride andsilicon oxide. The anti-reflection layer 50 c is made of organicmaterials used for organic bottom anti-reflection coating such aspolyimide and the like. Additionally, the anti-reflection layer 50 c canalso be made of inorganic materials used for inorganic bottomanti-reflection coating such as silicon oxynitride (SiON). Theanti-reflection layer 50 c can prevent incident light from reflectingfrom the substrate to the composite photoresist structure 50. Thus, dueto the anti-reflection layer 50 c, forming a standing wave in the secondorganic layer 50 d is avoided. The second organic layer 50 d is made oforganic photoresist materials that comprise positive photoresistmaterials and negative photoresist materials. As mentioned above, thecomposite photoresist structure 50 can be utilized in anyphotolithography processes. It should be known by one skilled in the artthat a thickness of each of the first organic layer 50 a, thesacrificial layer 50 b, the anti-reflection layer 50 c, and the secondorganic layer 50 d could be adjusted according to requirements ofprocesses. However, in this embodiment, the first and second organiclayers 50 a, 50 d are both thicker than the sacrificial layer 50 b,while the sacrificial layer 50 b is thicker than the anti-reflectionlayer 50 c. In addition, the first organic layer 50 a is thicker thanthe second organic layer 50 d.

In comparison with the prior art, the present invention provides acomposite photoresist structure including a first organic layer, aninorganic sacrificial layer, and a second organic layer. A thickness ofthe second organic layer could be adjusted according to wavelengths oflight sources used in exposure processes. Simultaneously, by adjustingthicknesses of the sacrificial layer and the first organic layer, thecomposite photoresist structure is thick enough to block ensuing etchingprocesses. Thus, the claimed photoresist structure is suitable forsub-micron pattern transfers in semiconductor processes. As a result,the predetermined pattern of the mask can be accurately transferred ontothe semiconductor wafer, and a critical dimension (CD) is thereforecontrolled well. In addition, the first organic layer is regarded as ahard mask and it is easily removed through use of plasma. It is also anadvantage that removing the first organic layer will not damage thesubstrate.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A composite photoresist structure, comprising: a first organic layerdisposed over a substrate to be etched; a sacrificial layer disposed onthe first organic layer; and a second organic layer disposed on thesacrificial layer; wherein a thickness of the first organic layer and athickness of the second organic layer are both larger than a thicknessof the sacrificial layer.
 2. The composite photoresist structure ofclaim 1 wherein the thickness of the first organic layer is larger thanthe thickness of the second organic layer.
 3. The composite photoresiststructure of claim 1 further comprising an anti-reflection layerdisposed between the sacrificial layer and the second organic layer. 4.The composite photoresist structure of claim 3 wherein the thickness ofthe sacrificial layer is larger than a thickness of the anti-reflectionlayer.
 5. The photoresist structure of claim 3 wherein theanti-reflection layer is made of organic anti-reflection materials. 6.The photoresist structure of claim 5 wherein the anti-reflection layeris made of polyimide.
 7. The photoresist structure of claim 3 whereinthe anti-reflection layer is made of inorganic anti-reflectionmaterials.
 8. The photoresist structure of claim 7 wherein theanti-reflection layer is made of silicon nitride or silicon oxynitride.9. The composite photoresist structure of claim 1 wherein the substratecomprises silicon, metal, or dielectric materials.
 10. The compositephotoresist structure of claim 1 wherein the first organic layer is madeof an organic material that is easy to be removed by means of plasma,thereby avoiding damage of the substrate to be etched during a patterntransferring process.
 11. The composite photoresist structure of claim10 wherein the first organic layer is made of low dielectric organicmaterials.
 12. The composite photoresist structure of claim 10 whereinthe first organic layer is made of SOG.
 13. The composite photoresiststructure of claim 10 wherein the plasma is selected from the groupconsisting of oxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon (Ar),C_(x)F_(y), C_(x)H_(y)F_(z), and helium (He) plasma.
 14. The compositephotoresist structure of claim 1 wherein the sacrificial layer is madeof inorganic anti-reflection materials.
 15. The composite photoresiststructure of claim 1 wherein the sacrificial layer is made of siliconnitride, silicon oxide, or silicon oxynitride.
 16. The compositephotoresist structure of claim 1 wherein the second organic layer ismade of an organic photoresist material capable of absorbing light witha wavelength of 248 nm and the less.
 17. The composite photoresiststructure of claim 1 wherein the second organic layer is suitable for ane-beam lithography process.
 18. The composite photoresist structure ofclaim 1 wherein the substrate has a planar and smooth surface.
 19. Thecomposite photoresist structure of claim 1 wherein the compositephotoresist structure is used for transferring a pattern onto thesubstrate to be etched.